1. Field of the Invention
This invention relates generally to a cover for a medical ultrasonic imaging probe. More particularly, this invention relates to a probe cover having a reservoir for containing a quantity of ultrasonic imaging gel, the reservoir bounded by a deformable membrane which is flexible by contact with the probe upon insertion into the cover. Deformation of the membrane expels a portion of the gel through the membrane, into contact with the probe. The remainder of the gel stays in position within the reservoir, thereby assuring constant ultrasonic contact between the probe and the cover.
2. Description of Related Art
Ultrasonic imaging is used in the medical field for a number of applications requiring non-invasive observation of internal anatomical tissue and structures. One common application of ultrasonic imaging is to monitor the development of a fetus during pregnancy. Ultrasonic imaging is also frequently used in pre-surgical diagnosis of internal organs, and to locate tissue and organs during laparoscopic surgery.
An ultrasonic probe having one or more transducer elements, or crystals, is typically used to transmit and receive ultrasonic signals directed to the tissue of interest. The signals are processed to generate a visual display, commonly on a video monitor. Due to the expense of the probes, it is necessary that the probes be reused for examining many patients. The construction of the probes, however, renders them difficult, if not impossible, to effectively sterilize between successive uses. Therefore, a disposable, sterile probe cover or sheath is typically placed over the probe prior to use with each patient, and discarded after the examination is complete.
In order to achieve good ultrasonic imaging, it is necessary that ultrasonic contact or coupling be maintained between the probe and the target body or tissue to be observed. The use of a probe cover can adversely affect this ultrasonic contact if air pockets or other non-ultrasonically transmissive voids come between the cover and the probe. In order to maintain ultrasonic contact between the probe and the cover, ultrasonically transmissive gel is placed between the probe and the cover. It has been found that application of too much or too little of the gel between the probe and the cover will cause ultrasonic reverberation artifacts which degrade the image quality. Therefore, with known covers, it is necessary to closely control the quantity of gel applied.
Several types of probe covers are presently available. One variety is a thin-walled, flexible, tightly-fitting condom made of an elastomeric material such as latex rubber. In use, a quantity of ultrasonic gel is placed loosely inside the tip of the condom, and the condom is then stretched over the probe and secured with rubber bands or plastic clips. Several disadvantages have been found to result from the use of this type of probe cover. First, as described above, the quantity of gel introduced into the cover must be closely controlled to insure good imaging. This is time consuming and requires some amount of guesswork. Another disadvantage of this type of probe cover is that the gel is often displaced out of the tip area during the installation of the cover onto the probe, and/or during use. For example, the gel often slides down the sides of the probe as the cover is stretched over the probe or as the probe is moved along the outer surface of the target body, leaving an insufficient quantity of gel around the tip of the probe. Problems are also encountered with this type of probe cover due to the clips or rubber bands used to secure the cover to the probe. Rubber bands tend to break while scanning, allowing the probe cover to shift on the probe, thereby causing imaging quality to deteriorate. The outwardly-extending tips of the plastic or metal clips sometimes used to secure the covers often cause pain or discomfort to the patient. Still another disadvantage of this type of probe cover is that their manufacturers often apply a powder such as talc to the condoms to prevent their sticking together. These powders may contain embryotoxic compounds, rendering the use of these covers incompatible with transvaginal egg retrieval procedures.
Another type of known probe cover is a loose-fitting, thin-walled, sleeve made of flexible material such as polyethylene. These covers are typically installed by placing a quantity of ultrasonic gel either on the tip of the probe or in the tip end of the cover, inserting the probe into the cover, and securing the cover to the probe with clips or rubber bands. This type of cover suffers the same types of disadvantages as described above. In addition, the loose fitting nature of these covers lends to the possibility of the shifting of the cover on the probe and/or the shifting of the gel within the cover during installation and use.
U.S. Pat. No. 5,335,663 to Oakley, et al. discloses a sheath for covering an ultrasonic probe which sheath includes a chamber at its tip for containing an ultrasonically transmissive medium. The chamber is described as partitioned from the remainder of the sheath's interior by a thin membrane which is ruptured when the probe is inserted into the sheath. The Oakley, et al. sheath may address the disadvantage discussed above, regarding the necessity of accurately measuring the proper quantity of ultrasonic gel applied between the probe and the cover. Also, at least to some extent, the Oakley, et al. sheath may successfully retain the gel in the tip region of the sheath during installation of the sheath onto the probe. Several known disadvantages, however, remain unaddressed by the Oakley, et al. sheath. For instance, once the probe ruptures the membrane, the gel is no longer constrained in place in the region of the probe tip, and may be displaced by further use of the probe. This can result in an insufficient amount of gel in the area of the probe tip for good ultrasonic imaging, and can allow a loss of ultrasonic contact between the cover and the probe. Additionally, the Oakley, et al. sheath is described as rigid and attached to the probe by the latching of a protrusion and a corresponding recess. This requires the sheath to be dimensioned for a close fit to a particular probe, thereby sacrificing the ability to provide a cover for general application to a number of probes having different external geometries. Rigid sheaths are also more expensive than flexible sheaths, and can interfere with the use of the probe in many applications. Oakley, et al. also does not address the above-described disadvantages of known devices for securing flexible-walled probe covers to a probe.
Thus, it can be seen that a need exists for a probe cover which eliminates the necessity for measuring the quantity of ultrasonic gel applied, and assures that the proper quantity of gel necessary for good ultrasonic imaging is utilized. A further need exists for a probe cover which maintains the proper quantity of gel in position over the transducer portion of the probe throughout the installation and use of the cover, and which maintains ultrasonic contact between the probe and the cover and between the cover and the target body. The need further exists for a probe cover that can be securely attached to a probe, reducing or eliminating the possibility that the cover will shift on the probe during installation and use, and including secure attachment means that will not cause discomfort to the patient. It is to the provision of such a device that the present invention is primarily directed.